"Bombardier reserves all its rights with regard to these defamatory accusations," the company said.

DB is suing Bombardier for 350 million euros, or roughly $455 million, in damages, citing defective brakes and engines, which it says has occurred regularly since 2009. Out-of-court efforts by the two entities to settle the matter were attempted, but failed.

The supplier said the general warranty for the S-Bahn Berlin 481 series ended in 2007 by mutual agreement. Up to that time, Bombardier said, availability had regularly exceeded 98%, favorable compared with similar rail systems in Europe. From the start, S-Bahn Berlin has been responsible for its own maintenance. Bombardier Transportation has no contractual obligations regarding the maintenance and repair of the 481 series, the company said.

Bombardier Transportation believes that prolonged litigation is not in the interests of either company, and stressed that it remains open to dialogue with DB.